PROJECT SUMMARY/ABSTRACT Alzheimer?s disease (AD), the most common form of dementia, is the third leading cause of death for older people in the US, and currently affects 5.5 million Americans. The cost of care for AD and other dementias is at an estimated $277 billion in 2018. Despite extensive investigation of AD pathogenesis and significant investment in developing therapeutics for AD, no cure is currently available ? there is an urgent need to accelerate research to develop effective treatments. At the molecular level, AD is a protein disease. Decades of studies have established crucial roles for the formation and deposition of b-amyloid protein (Ab), the aggregation and propagation of the Tau protein, and a variant of the ApoE protein in different stages of AD pathogenesis. However, therapies targeting these proteins have yet to be successfully developed. Filling the knowledge gaps of AD onset and progression along its progressive pathways from the presymptomatic stage to irreversible degeneration and death of neurons will be crucial for development of effective treatments against Alzheimer?s. Aiming to fill these knowledge gaps and to broaden knowledge of AD-associated factors beyond Ab, Tau, and ApoE, this project seeks to discover new AD proteins, pathways, and networks. Built upon strong preliminary data obtained with ultra-deep multilayer proteomics analysis of longitudinal human AD brains and mouse models, three specific aims are proposed to (1) identify AD protein networks and their components using an integrated proteomics and systems biology approach, (2) refine AD pathways by mapping the interactomes of the top AD proteins identified in the preliminary studies, and (3) test whether Netrin-1, a top candidate AD protein identified in preliminary work, is a neuroprotective factor during AD progression. The novel AD proteins, pathways, and networks discovered and validated in this project will lead to a deeper, broader, and more precise understanding of AD progression at the molecular levels and will serve as a rich source for finding new biomarkers and drug targets for Alzheimer?s diagnosis and treatment.